# include "udf.h"
DEFINE_CG_MOTION(piston, dt,vel,omega, time, dtime)
{
    NV_S(ve1,=,0);
    NV_S(omega,=,0);
if(time<1)
      ve1[1]=0.1;
if(time<2)
       ve1f1]=-0.1;
}